This invention relates to an apparatus for explosively forming a tube into a bore formed in a tube sheet, and more particularly, to such an apparatus utilizing an explosive which is placed within the tube to be expanded.
Many current designs of heat exchangers feature the use of a plurality of heat exchange tubes disposed within bores extending through a tube sheet. The tubes receive a primary fluid which is passed through the tubes in a heat exchange relationship with a secondary fluid passing over the tubes.
Various techniques have evolved for securing the tubes within the tube sheet. For example, the tubes have been mechanically expanded into the tube sheets utilizing a mandrel or the like, or by rolling, i.e., by applying an outward radial force against the entire surface of the tubes. However, these techniques enjoy several disadvantages including local metal deformation, general lengthening of the tubes, and the application of axial stresses on the tube weld and compressive strains in the tube wall.
In order to overcome the foregoing disadvantages, a technique of explosively forming the tubes within the tube sheet has evolved. According to this technique, an explosive charge is disposed within the area of overlap between the tubes and the tube sheet and is surrounded by a force-transmitting member which, upon detonation of the explosive charge, expands the tube uniformly against the inner wall of the tube sheet.
Recently there has been much interest in using explosive expansion of the above type to repair tube-tube sheet joints in nuclear steam generators. However, as a result of the explosion, the polyethylene force-transmitting member fractures, leaving debris which must be removed from the tubes prior to their reuse. In addition, the gases generated by the explosive are not contained and are allowed to travel down the tube carrying along vaporized polyethylene. This contamination, because of the levels of radiation, is extremely costly to remove.